The present invention relates to a thermal transfer sheet. More particularly, the present invention is concerned with a thermal transfer sheet which enables repeated printing cycles to be conducted in an identical region.
In an output print of a computer or a word processor by a thermal transfer system, use has hitherto been made of a thermal transfer sheet wherein a heat-meltable ink layer was provided on one surface of a substrate film.
The conventional thermal transfer sheet is produced by coating a heat-meltable ink layer of a mixture of a wax with a colorant, such as a pigment or a dye, on a substrate film comprising a paper such as a condenser paper or a paraffin paper having a thickness of 10 to 20 .mu.m or a film of plastic such as polyester or cellophane. The most serious problem of the thermal transfer sheet is that printing can be conducted only once in an identical region, which is very disadvantageous from the viewpoint of economy. Specifically, in the case of an ink ribbon for a typewriter comprising a commonly used fabric tape impregnated with an ink, printing can be conducted twice or more in an identical region. On the other hand, in the case of a thermal transfer sheet, since the whole ink layer is transferred by single printing, printing cannot be conducted twice or more in an identical region, so that the substrate sheet used in a thermal transfer sheet is discarded after it is used only once. The amount of an ink actually transferred in a transfer material occupies only several %, ten-odd % at the highest of the whole ink, and the remaining majority part of the ink is discarded without use.
Accordingly, an object of the present invention is to solve the above-described problem and to provide a thermal transfer sheet which enables printing to be conducted twice or more in an identical region.